Reflector for use in light-projectors



J. G. BALSILLIE.

REFLECTOR FOR USE IN LIGHT PROJECTORS.

APPLICATION FILED NOV. 16. 1920.

Ana}.

1,390,747. PatentedSept. v13, 1921..

UNITED STATES PATENT OFFICE.

FLATLITE LIMITED, OF SYDNEY, NEW SOUTH TION OF NEW SOUTH WALES.

WALES, A STRALIA, A CORPORA- REFLECTOR FOR USE IN LIGHT PRO-TECTORS.

Specification of Letters Patent. Patented Sept, 13, 1921,

Application filed November 16, 1920. Serial No. 424,530.

To all whom it may concern.

.Be it known that JOHN GRAEME BALSIL- LIE, subject of the King ofGreatBritain. residing at Collins House, 360-366 Collins street,Melbourne, Victoria, Australia, has invented certain new and usefulImprovements in Reflectors-for use in Lightlrojectors, of which thefollowing is a specification. This invention relates to improvements inreflectors for use in light projectors more particularly adapted fortheheadlamps of vehicles such as motor cars and' the like.

Though this invention is herein described as being adapted for theheadlamps of motor cars, it will be understood that it is applicable forthe head lights of locomotives, tramcars and the like, and is alsoadaptable for the projection of light for other purposes such as streetlighting.

It is known'that when aroadway in front of a road vehicle is brilliantlyilluminated by non-diffused light, the driver or an observer has greatdifficultyin seeing objects immediatelybeyond the area of brightillumination. The reason for this is that the brilliantly illuminatedpath of roadway in tereferes with the resolving power of the It has longbeen known that more satisfactory road illumination can be achieved bydiffused lighting but hitherto this type of illumination hasbeen-usually Chat acterized by glare which interferes with the vision ofof light.

The object of the present invention is to provide means whereby lightmay be diffusely reflected and projected preferably in a beam ofelliptical crosssection substantially. v

I accomplish thisobject by providing the reflecting surface of areflector with configurations which function to reflect. light diffusely"in one plane and substantially regularly in the planeat i-ight anglesthere to i persons looking toward the source This is effected byprovidingthe reflecting surface of the reflector with parallelcorrugations. grooves, or furrows.

' of the chief meridians and a. source of light is placed at or aboutthe focal point of that chief meridian with which the configurations areparallel diffused light is projected in relatively parallel rays in oneplane and divergent or convergent divergent rays in the plane at rightangles thereto.

Vi hen such configurations are applied to the reflecting surface of anastigmatic reflector, preferably t right angles to its principalmeridian and a source of light is placed at or about the focal point ofthe shortest principal meridian light is pro-' jected in relativelyparallel rays in the plane of one meridian and divergent or convergentdivergent rays in the plane of the other meridian.

The plane inwhich the light is projected in substantially parallel rayscoincides with the plane of that meridian of the reflector witlll whichthe said configurations are paralle The type of configuration that Ifind most satisfactory is regularly parallel corrugations, furrows, orgrooves, which may be of varying frequency and radius, but preferably ofabout 35 to an inch, each corrugation having a radius of curvature ofseven thirty seconds of an inch. In this specification, the termcorrugations will be understood to include furrows or grooves. Thesecorrugations made on the reflecting surface function to give a regularlyastigmatic effect to a stigmaticreflector. When the invention is adaptedto a regular astigmatic reflector the corrugations are made parallelwith one or other of the principal better understood, I will now proceedto describe same by reference to the accompanying sheet of drawings, inwhich,

Figure 1 is an elevation, and

Fig. 2a cross section of a regularly astigmatic reflector which has beenconfigurated in accordance with this invention,

such configurations being in the form of corrugations parallel to thesmallest principal meridian.

Fig. 3 is a vertical sectional elevation of a motor head lamp fittedwith a reflector as shown'in Figs. 1 and 2.

Fig. 4 is a front elevation of a stigmatic parabolic reflector asordinarily in use which has been conflgurated in accordance with thispresent invention such configurations being in the form of parallelcorrugations.

. Figs. 5, 6, and 7, are sections of a portion of a reflector to whichcorrugations of different configurations have been applied for thepurpose of this invention.

In these drawings A represents the reflector within which is fitted thesource of light B (such as an electric lamp) adapted to fit within thesocket C.

In Figs. 1, 2, and 3, a regular astigmatic reflector is shown, and thismay bemounted .cause the corrugations only operate to diverge the lightprojected in a plane at right angles to the plane of the corrugations.The

source of light should be located at or about the focal point of thatmeridian of the reflector which is parallel with the plane of thecorrugations.-

-The corrugations are made parallel with one of the chief meridians ofthe reflector and may be made to function to accentuatethe astigmatism-By varying the radius of these corrugations and their frequency, theamount of divergence can be altered to suit different conditions. Forexample, satisfactory results have been obtained with corru-.

gations in which the radius of. curvature and frequency have been of thefollowing dimensions Curvature radius in Frequency per inches. inch.Seven thirtyseconds. Thirtyfive. Twelve thirtyseconds. Fifteen. Tenthirtyseconds. Twentyfive. Six thirtyseconds. Fortyfive.

The invention is applied in a similar mannor to reflectors of all typeswherein all meridians are curves by configuring the reflecting surfaceas shown in Fig. 4- with a series of parallel corrugations.

In astigmatic reflectors the corrugations are preferably at right anglesto the principal meridian. The corrugations may be con caval as shown inFig. 5 or convexo-concaval as shown in Fig. 6, or in the form of Vshaped depressions as shown in Fig. 7.

I claim 1. A reflector having its reflecting surface provided withparallel corrugations arranged to project light in relatively parallelrays in one plane and divergent rays in the plane at right anglesthereto.

\ 2. A reflector for use in light projectors having its reflectingsurface provided with corrugations parallel with one meridian.

3. A reflector for use in light projectors in which all the meridiansare curves of graduating focal lengths having its reflecting surfaceprovided with corrugations at right angles to the principal meridian.

4. A reflector for use in light projectors in which all the meridiansare curves of graduating focal lengths and in which the chief meridiansare mutually at right angles and the values of the intermediatesemicurves in each quadrant decreases uniformly from the largest to thesmallest having its reflecting surface provided with corrugationsparallel with one of the said chief meridians.

5. In light projectors a reflector having the reflecting surfaceprovided with corrugations parallel with one meridian and a source, oflight placed at or about the focal point of that meridian.

6. In head lamps for vehicles, a reflector having its reflecting surfaceprovided with corrugations arranged with the planes of the corrugationssubstantially perpendicular to the surface of the roadway and parallelwith one meridian.

In testimony whereof he has affixed his signaturev in the presence oftwo witnesses.

JOHN GRAEME BALSILLIE.

lVitnesses:

CLEM A. HACK, G. I). ALLEN.

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